Color liquid crystal displays (LCDs) are usually made by putting color filters onto the individual pixels of a liquid crystal display. These color filters are resins with color pigments. Full color displays can be made by a combination of the red, green and blue primary colors. This coloring scheme is the predominant technology for active matrix as well as passive matrix LCDs currently in use. Many colors can be obtained.
For many applications, multiple colors rather than a full range of colors may be sufficient. This is especially true for low cost products not requiring full video displays. There have been several proposals to produce a color effect without the use of color filters. The advantages of colors without color filters are many, the most important one being cost and ease of manufacturing. Yamaguchi et al, Yamaguchi et al and Yang et al teach the generation of color by the addition of a birefringent film inside the LCD. The birefringence color is due to the interference effect and dispersion effect of the transmission of the LC cell. While most of the attention is concentrated on the supertwisted nematic (STN) display with a twist angle of larger than 180°, there is nevertheless a need for similar techniques for low twist angles. Such displays have not been studied systematically.